1. Field of the Invention
The subject invention generally pertains to electronic power conversion circuits, and more specifically to high frequency, switched mode power electronic converter circuits.
2. Description of Related Art
Several circuits have been invented that provide advantages for high frequency power conversion. At high switching frequency, transistor switching losses become a limiting factor, unless a mechanism is provided that inherently reduces or eliminates switching losses. One of these circuits, illustrated in FIG. 1, is the subject of U.S. Pat. No. 6,259,235. The FIG. 1 circuit is a zero voltage switching (ZVS) cell, which when substituted for the main rectifier in a power conversion circuit that contains a single main rectifier, provides a mechanism for driving a zero voltage turn on transition for the power converter""s main switch. An example of the use of the FIG. 1 circuit in a boost converter is illustrated in FIG. 2. One minor limitation of the FIG. 2 circuit is that the auxiliary switch cannot be driven directly by a simple ground referenced circuit. Integrated circuits (ICs) exist for controlling circuits of the type illustrated in FIG. 2 in which an auxiliary switch operating in anti-synchronization to the main switch is required. The available IC controller chips provide a drive signal suitable for driving a mosfet that is referenced to ground. In order to drive the auxiliary switch of the FIG. 2 circuit either a gate drive transformer or a high side driver circuit would typically be provided. What is needed is a zero voltage switching cell that performs in a manner similar to the FIG. 1 switching cell that can be driven directly from the ground referenced drive circuits included in the available active reset controller ICs without the requirement of a gate drive transformer or a high side driver circuit.
The active reset switching cells that exist all have one trait in common, the existence of an auxiliary switch operated in anti-synchronization to a main switch and all of these include a capacitor in series with the auxiliary switch which is used to exchange energy with a small magnetic circuit element in order to reverse the direction of a current in the circuit which is used to drive a zero voltage turn on transition of a main switch. When these active reset switching cells are used in a power converter with bi-directional power flow the role of main switch in the converter changes with the direction of power flow. In one direction of power flow one switch (or pair of switches) is a main switch and another switch (or pair of switches) is a synchronous rectifier until the power flow direction reverses and then the roles of the switches reverse and what were the synchronous rectifiers become the main switches and what were the main switches become the synchronous rectifiers. In order to accomplish zero voltage switching for both directions of power flow one can use an active reset circuit for each switch. What is needed is a method that can accomplish zero voltage switching in bi-directional power flow converters with fewer switches and less circuitry. A solution with a single auxiliary switch, a single capacitor, and a single small magnetic circuit element would be ideal.
Simple isolated power converters that accomplish zero voltage switching have become well known and commercially successful. A good example of one of these, illustrated in FIG. 26, is the subject of U.S. Pat. No. 5,402,329. Improvements to these original circuits, one example of which is illustrated in FIG. 27, integrates an input filter with the active reset circuit. New circuit synthesis methods that enhance the electromagnetic compatibility of power converter circuits have been developed. These benefits improve with the number of windings available in the original circuit since the benefits largely result from putting uncoupled magnetic flux to good use. What is needed is a simple circuit similar to those cited with windings balanced on both sides of the isolation boundary.
Adaptive gate driver circuits for zero voltage switches have been invented which provide optimal timing for turn on of zero voltage switches. An example of one of these circuits is illustrated in FIG. 31. The FIG. 31 circuit senses when the voltage across the switch has dropped to zero and then immediately provides gate energy to turn on the switch. One problem associated with these zero voltage switch drive circuits is that, in many cases, there are line and load conditions in which there is insufficient energy available to drive a zero voltage turn on transition. In these cases the turn on timing is typically determined by some fixed delay. In the FIG. 31 circuit the fixed delay is determined by the R2 resistor and the input capacitance of the N channel mosfet switch, but this delay may not be optimal, as illustrated in FIG. 32(b), where the delay results in the switch turning on after the switch voltage has reached a minimum and has begun to rise up above its minimum. A circuit that enables the gate drive energy at the minimum switch voltage is needed.
Coupled magnetic circuit element structures that reduce ripple currents in multi-phase interleaved power converter circuits have been invented. Originally these involved placing the windings on the outer legs of E core structures and gapping the center legs to provide a shared energy storage leg and tighter magnetic coupling between the outer leg windings. An example of such a structure, its magnetic circuit equivalent, and electrical equivalent are illustrated in FIGS. 45, 46, and 47, respectively. Until recently no similar structures applicable to more than two phases were revealed. FIG. 48 reveals a structure that shares some of the advantages of the FIG. 45 structure for 4 phases. The magnetic equivalent circuit is illustrated in FIG. 49. There are two shortcomings of the FIG. 48 arrangement. The first shortcoming results from the lack of a defined path for return flux resulting in flux returning along the full length of the top and bottom legs through the window areas. Returning flux through the window areas results in eddy current losses in the copper residing in the window areas. Another problem is the asymmetry that results in good coupling between adjacent legs, poor coupling between legs that are not adjacent, and, for practical purposes, non-existent magnetic coupling between the two outer legs. What is needed is a simpler scheme that provides better balance and symmetry for more uniform coupling and better mutual flux ripple cancellation.
An object of the subject invention is to provide a ZVS cell that eliminates first order switching losses in all switches applicable to a wide variety of power converter types.
Another object of the subject invention is to provide a ZVS cell that can be driven directly by the commercially available active reset controller ICs without the use of any kind of high side gate drive mechanism.
Another object of the subject invention is to provide a ZVS cell that distributes the ZVS drive energy between main switch and rectifier circuits thereby creating a circuit to which known synthesis methods can be applied to achieve new ZVS circuits with enhanced electromagnetic compatibility on both sides of an isolation boundary.
Another object of the subject invention is to provide a simple active reset mechanism applicable to ZVS cells in bi-directional power flow converters.
Another object of the subject invention is to provide a gate drive circuit with optimal switch timing for both energy sufficient and energy insufficient turn on transitions.
Another object of the subject invention is to provide a ZVS dc to dc transformer circuit with a simplified low volume magnetic circuit element structure.
Another object of the subject invention is to provide a primary switch network with low winding voltage stress so that fewer primary turns are required and planar magnetic structures can be more easily accommodated.
Another object of the subject invention is to provide simple multi-phase converter cells with coupled magnetic circuit elements that achieve reduced ripple current and faster transient response.
Another object of the subject invention is to provide integrated magnetic structures suitable for use with multi-phase power converters that achieve high mutual coupling between converter phases for lower ripple current and faster transient response.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
These and other objects of the invention are provided by novel circuit techniques and circuit element structures.